Field of the Invention
The present invention relates to an imaging optical system suitable for an optical apparatus such as an image pickup apparatus and an image projection apparatus.
Description of the Related Art
An imaging optical system that combines a refractive optical system with a reflective optical system to achieve especially a wide angle has been known. Japanese Patent No. 3727543 discloses an imaging optical system that combines a refractive optical system of a retrofocus type with a convex mirror as a reflective optical system. Japanese Patent No. 4223936 also discloses an imaging optical system that combines a refractive optical system of a retrofocus type with a concave mirror having a positive power as a reflective optical system.
However, in the imaging optical systems disclosed in Japanese Patent No. 3727543 and Japanese Patent No. 4223936, since an off-axis lay should be strongly bent according to a wider angle, large distortion easily occurs. Using a large-diameter mirror and a large-diameter lens is required to properly correct it.
To solve the above problem, an imaging optical system disclosed in Japanese Patent No. 5484098 forms an intermediate real image inside a refractive optical system to reduce a diameter of a convex mirror disposed on the most enlargement side conjugate surface side.
However, the imaging optical system disclosed in Japanese Patent No. 5484098 fails to properly set a power ratio of the refractive optical system to the convex mirror, and thus cannot excellently correct various aberrations such as distortion, a field curvature and a chromatic aberration of magnification.